Re: [foxboro] Floating point data via FBM 224

Floating point in FBM224 Modbus uses the format tAxxxxxFyWz for PNT_NO
of the RIN block.

In order to satisfy myself of the bit-order of the bytes in the floating
point value to be read, I always build a temporary PAKIN to look at the
raw bits. Once you get one value built properly, the rest are easy.

You build up PNT_NO (tAxxxxFyWz) as follows:
t is the transaction code from the device configurator
Axxxxx is the point address (either 4 or 5 digit addressing)
Fy is the number of bytes in the floating point value to be read
Wz is whether the bytes need to be swapped (hence the PAKIN)

1A33001F4 reads a 4-byte (32-bit) floater at address 33001 with no byte
swapping
1A33001F4W1 reads the same value but reverses the order of all 4 bytes
1A33001F4W2 reads the same value but flips bytes 1/2 and 3/4

The swapping codes are detailed in Tables 5-5 to 5-8 of B0400FK
The key is to look at the PAKIN and see what order the bytes are in,
then use the proper W code to restore them.

Brad Wilson
brad.wilson@xxxxxxxxxxxxxxxx
Invensys Process Systems, Inc
1090 King Georges Post Rd, Suite 204
Edison, NJ  08837
732-661-4012 o
732-874-0087 c
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Gregory A Hurwitt
Sent: Tuesday, July 22, 2008 5:55 PM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Floating point data via FBM 224

I am trying to read floating point data from a Triconex system (Tricon
V9.x) with an FBM 224.  Data is in Memory/Real/Read-only addresses in
the
Tricon (Modbus alias numbers 33xxx).  The "Example for Reading a
Floating-Point Input" in document B0400FK hasn't been much help.


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